The present invention pertains to the homogenous incorporation of fillers into rubber, and more particularly to a process for the preparation of rubber containing carbon black of a very small and uniform particle size that is highly and uniformly dispersed.
Rubber products, such as vehicle tires and seals are made typically by compounding or mixing fillers, such as carbon black or silica, into rubber, which is then vulcanized. For vehicle tires, additional structural properties are introduced by embedding cords and by using different types of rubber in the tread, side wall and interior lining.
A manufacturer, such as a tire manufacturer, typically receives its raw material from different sources. Rubber is received as bales or possibly as a crumb or as a powder. A rubber manufacturer is located typically geographically separated by a considerable distance from its customer, the tire or rubber product manufacturer. The rubber is transported over considerable distances typically by rail or truck.
A carbon black manufacturer is typically located geographically distant from both the tire or rubber product manufacturer and the rubber manufacturer. Several processes are available for making carbon black, including a thermal black process, an acetylene black process, a lampblack process, an impingement or channel process, and an oil-furnace process. The oil-furnace process is used typically for making carbon black, and in any of these processes, an intermediate is made called fluffy carbon black.
Fluffy carbon black is very difficult to handle. It comprises particles so fine that the particles are measured in nanometers (nm), and it has a very low bulk density. Fluffy carbon black is typically pelletized with the addition of water and an agglomerating agent to yield a pelletized product that can be handled. Other types of agglomerates such as granules, powder and beads can be used. The wet pellets are dried, typically in rotary drums, and dry pellets are transported by truck or rail in bags or the like to the tire or rubber product manufacturer.
The tire or rubber product manufacturer receives the dry pellets and grinds the pellets by mechanical means to essentially as small a particle size as can be practically achieved. The ground carbon black typically has a particle size ranging between about 0.5 microns and about 45 microns. The ground carbon black is mixed with the rubber in a process called dry compounding. Mechanical mixing is used in the dry compounding process to intimately mix the carbon black with the rubber.
Alternatively, the dry pellets of carbon black are transported to a rubber manufacturing plant, which is typically geographically separated from the carbon black plant by a considerable distance. At the rubber plant, the dry pellets of carbon black are ground into as small a particle size as is practical using essentially the same grinding process as would otherwise have been used at the tire or rubber product manufacturer. The ground carbon black has a particle size distribution ranging between about 0.1 microns and about 7 microns.
The dry ground carbon black is mixed with water to form a slurry that is added to an intermediate step in the process for making the rubber, typically in a coagulation step. The carbon black is mixed with the rubber as the rubber is made, resulting in a product called black masterbatch. Black masterbatch is thus a rubber product that already has carbon black dispersed through it. The black masterbatch can be handled and transported to the tire or rubber product manufacturer in bales or as crumb or dry powder in the same manner as rubber without carbon black can be handled and transported.
A rubber manufacturing plant that makes black masterbatch typically uses styrene and butadiene as raw materials although other types of rubber can be used, such as acrylonitrile and butadiene. One of two processes is typically used for making rubber from styrene and butadiene. One process is called emulsion styrene-butadiene rubber (ESBR), and the other process uses organolithium compounds in an ionic polymerization for making what is called solution styrene-butadiene rubber (SSBR). Fillers are typically added to rubber, and the most common filler is carbon black since it is a reinforcement agent as well as a filler.
Mechanical and rheological properties of rubber are influenced by different factors that can vary from the styrene-butadiene ratio to the way in which vulcanization is performed, whenever these are vulcanized. Naturally, the amount and the way in which carbon black is incorporated into the rubber also affect the final properties of materials.
A process is provided for making a carbon-filled rubber that includes the steps of forming a rubber intermediate; adding a fluffy carbon black stream to the rubber intermediate; incorporating fluffy carbon black to form a rubber having carbon black dispersed therethrough; and processing the mixture of carbon black and rubber to form a carbon-filled rubber. In one embodiment the rubber intermediate is a latex in an emulsion styrene-butadiene plant. The fluffy carbon black stream is preferably received as a slurry of fluffy carbon black in water; and optionally, a dispersant can be added to aid in dispersing the fluffy carbon black in the water to form the fluffy carbon black slurry. The dispersant is preferably a naphthalenesulfonate composition although other dispersants can be used. Preferably, the average particle size of the fluffy carbon black intermediate is less than about 1000 nm when dispersed in water, and/or about 95% of the carbon black particles may be less than 2000 nm.